REVIEW Open Access

Porcine epidemic diarrhea virus: Anemerging and re-emerging epizooticswine virusChanghee Lee

Abstract

The enteric disease of swine recognized in the early 1970s in Europe was initially described as “epidemic viraldiarrhea” and is now termed “porcine epidemic diarrhea (PED)”. The coronavirus referred to as PED virus (PEDV) wasdetermined to be the etiologic agent of this disease in the late 1970s. Since then the disease has been reported inEurope and Asia, but the most severe outbreaks have occurred predominantly in Asian swine-producing countries.Most recently, PED first emerged in early 2013 in the United States that caused high morbidity and mortalityassociated with PED, remarkably affecting US pig production, and spread further to Canada and Mexico. Soonthereafter, large-scale PED epidemics recurred through the pork industry in South Korea, Japan, and Taiwan. Theserecent outbreaks and global re-emergence of PED require urgent attention and deeper understanding of PEDVbiology and pathogenic mechanisms. This paper highlights the current knowledge of molecular epidemiology,diagnosis, and pathogenesis of PEDV, as well as prevention and control measures against PEDV infection. Moreinformation about the virus and the disease is still necessary for the development of effective vaccines and controlstrategies. It is hoped that this review will stimulate further basic and applied studies and encourage collaborationamong producers, researchers, and swine veterinarians to provide answers that improve our understanding ofPEDV and PED in an effort to eliminate this economically significant viral disease, which emerged or re-emergedworldwide.

Keywords: PED, PEDV, Review, Molecular epidemiology, Diagnosis, Pathogenesis, Preventive measures

BackgroundHistorical perspectiveIn 1971, British veterinary clinicians noted the appear-ance of a previously unrecognized enteric disease ingrowing and fattening pigs [1]. A clinical presentation ofwatery diarrhea was similar to symptoms of the porcinetransmissible gastroenteritis virus (TGEV) infection.However, in the latter case, nursing piglets were onlymildly affected. The disease, named epidemic viral diar-rhea (EVD), then spread to multiple swine-producingcountries in Europe. Five years later, TGE-like EVD re-emerged and in contrast to previous outbreaks, the dis-ease occurred in pigs of all ages including suckling pigs.Therefore, EVD in 1976 was classified as EVD type 2 in

order to differentiate it from the initial EVD type 1 con-dition [2, 3]. In 1978, scientists at the Ghent Universityin Belgium were the first research group, which partiallyfulfilled Koch’s postulates and described a coronavirus-like agent (CV777) as the causative pathogen. Fur-thermore, they provided evidence that this novel viruswas distinct from the two known porcine corona-viruses, TGEV and hemaggultinating encephalomyeli-tits virus [4, 5]. Since then, the EVD disease has beenknown as “porcine epidemic diarrhea (PED)”.Since the 1990s, PED cases have become rare in

Europe and PED virus (PEDV)-associated diarrhea hasbeen usually observed in adult pigs, whereas sucklingpiglets were generally spared or developed only mildsymptoms [6]. PED was first reported in Asia in 1982and since then it has had a great economic impact onthe Asian pork industry [7–11]. In contrast to thepresent situation in Europe, PED epizootics in Asia are

Correspondence: changhee@knu.ac.krAnimal Virology Laboratory, School of Life Sciences, BK21 Plus KNU CreativeBioResearch Group, Kyungpook National University, Daegu 41566, Republicof Korea

© 2016 Lee. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 InternationalLicense (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in anymedium, provided you give appropriate credit to the original author(s) and the source, provide a link to the CreativeCommons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Lee Virology Journal (2015) 12:193 DOI 10.1186/s12985-015-0421-2

more severe causing high mortality in neonatal pigletsand the disease has become an endemic pattern recently.However, despite a notorious reputation in Asian swine-producing countries, PED was not a well-known diseaseworldwide. For example, the disease had never occurredin the United States until 2013. In May 2013, PED sud-denly appeared in the United States and rapidly spreadacross the country, as well as to Canada and Mexico,causing deaths of more than 8 million newborn pigletsin the United States alone during a 1 year-epidemicperiod [12–15]. Subsequently, severe PED outbreaksrecurred in Asian countries including South Korea,Taiwan, and Japan [16–18]. PEDV has now emerged orre-emerged as one of the most devastating viral diseasesof swine in the world, leading to significant financialconcerns in the global pork industry.This paper is a brief review focusing on current under-

standing of the molecular biology, epidemiology, diagno-sis, and pathogenesis of PEDV, as well as controlstrategies to prevent PEDV infection.

ReviewThe virusPEDV genome and virion structuresPEDV, the etiological agent of PED, is a large-envelopedRNA virus, which is a member of the genus Alphacoro-navirus within the Coronaviridae family placed with theArteriviridae family in the order Nidovirales on the basisof similarities in genome organization and replicationstrategy [4, 6, 19]. The PEDV genome is approximately28 kb long with a 5’ cap and a 3’ polyadenylated tail andcomprises a 5’ untranslated region (UTR), at least 7open reading frames (ORF1a, ORF1b, and ORF2–6), anda 3’ UTR [20]. The two large ORFs 1a and 1b occupythe 5’-proximal two-thirds of the genome coding fornonstructural proteins (nsps). ORF1a translation yields areplicase polyprotein (pp) la, whereas ORF1b isexpressed by a −1 ribosomal frame shift (RFS), which C-terminally extends ppla into pp1ab. These ppla andpplab are post-translationally cleaved by internal prote-ases generating 16 processing end products, namednsp1–16. The remaining ORFs in the 3’-proximal gen-ome region encode four structural proteins expressedfrom the respective 3’-co-terminal nested set of subge-nomic (sg) mRNAs: the 150–220 kDa glycosylated spike(S) protein, 20–30 kDa membrane (M) protein, 7 kDaenvelope (E) protein, 58 kDa nucleocapsid (N) protein,and one accessory gene ORF3 (Fig. 1a) [6, 20–22].The PEDV genome is encapsulated by a single N pro-

tein, forming a long and helical coil structure that iswrapped in a lipid envelope containing 3 surface-associated structural proteins, S, M, and E (Fig. 1b).Enveloped virions are roughly spherical and pleomorphicwith a diameter ranging from 95 to 190 nm, including

the widely spaced, club-shaped, trimerized S projectionsmeasuring 18–23 nm in length [4]. PEDV has a buoyantdensity of 1.18 g/ml in sucrose and is sensitive to etherand chloroform. The virus is stable at 4–50 °C and is ab-solutely inactivated at pH values beyond pH 4–9 range[23]. Therefore, PEDV is inactivated by various acidic oralkaline disinfectants [24].

PEDV structural proteinsAmong viral structural proteins, the S protein of PEDVis the major envelope type I glycoprotein of the virion,which interacts with the cellular receptor during virusentry and stimulates induction of neutralizing antibodiesin the natural host [22, 25, 26]. In addition, it is associ-ated with growth adaptation in vitro and attenuation invivo [27]. Thus, the PEDV S glycoprotein is known to bean appropriate viral gene for determining the geneticrelatedness among PEDV isolates and for developingdiagnostic assays and effective vaccines [16, 26, 28–30].The M protein, the most abundant component of theviral envelope, is required for the assembly process andcan also elicit the production of protective antibodieswith virus-neutralizing activity [31, 32]. The small enve-lope E protein plays an important role during corona-virus budding, and coexpression of E and M proteinscan form spike-less coronavirus-like virions [33]. PEDVE and N proteins are found in the endoplasmicreticulum (ER) where they independently induce ERstress [34, 35]. The N protein has multiple functions inviral replication and pathogenesis in coronavirology [36].Generally, N proteins of coronaviruses interact with viralgenomic RNA and associate with other N protein mole-cules to protect the viral genome, serving as the criticalbasis for the helical nucleocapsid during coronavirus as-sembly [36]. The PEDV N protein also perturbs antiviralresponses by antagonizing interferon production, as partof the immune evasion strategy, and activates NF-κB[35, 37]. The product of ORF3, the only accessory genein PEDV, is thought to function as an ion channel andto influence virus production and virulence [38, 39].

PEDV-host interactionsCoronaviruses can infect a wide range of mammals,including humans, bats, and whales, and birds, but typic-ally they have a limited host range, infecting only theirspecific natural host. Furthermore, coronaviruses exhibita marked tropism for epithelial cells of the respiratoryand enteric tracts, as well as for macrophages [40–42].PEDV also has a restricted tissue tropism and replicatesefficiently in porcine small intestinal villous epithelialcells or enterocytes. Porcine aminopeptidase N (pAPN)predominantly expressed on the surface of epithelialcells of small intestine has been identified as the cellularreceptor for PEDV [43, 44]. The N-terminal region of

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the PEDV spike protein S1 domain is important for recog-nizing the pAPN receptor [45]. Thus, PEDV entry beginswith the binding to pAPN followed by internalization ofthe virus into target cells by direct membrane fusion, anda subsequent release of the viral genome into the cytosolafter uncoating to start the genome replication (Fig. 2). Inaddition to replicating in primary target cells from the nat-ural host, PEDV can grow in some African green monkeykidney cell lines (Vero and MARC-145) [46, 47]. Althoughit still remains to be determined whether APN acts as thefunctional receptor for PEDV on these cells, overexpres-sion of exogenous pAPN renders non-permissive cellssusceptible to PEDV infection. This observation suggestsa functional significance of the APN receptor density forPEDV propagation in cell culture [44]. A recent study alsorevealed that cell-surface heparan sulfate acts as theattachment factor of PEDV in Vero cells [48]. The

addition of trypsin is indispensable for the isolation andserial passages in Vero cells [28, 46, 49, 50]. Trypsin facili-tates PEDV entry and release by cleaving the S proteininto S1 and S2 subunits, enabling efficient viral replicationand spreading in vitro [51, 52]. However, some cell-adapted attenuated PEDV strains, such as SM98-1 and83P-5, can support PEDV propagation in the absence oftrypsin [44, 53]. As a result of viral infection, distinct cyto-pathic effects (CPEs) including cell fusion, vacuolation,syncytium, and detachment are produced in infected Verocells [49].Since viruses are obligate intracellular parasites, they

may adjust the activity of cellular factors or signalingpathways to benefit their own multiplication in hostcells. Proteome analysis showed that the expression ofproteins involved in apoptosis, signal transduction, andstress responses is affected in PEDV-infected Vero cells

Fig. 1 Schematic representations of PEDV genome organization and virion structure. a The structure of PEDV genomic RNA. The 5’-capped and3’-polyadenylated genome of approximately 28 kb is shown at the top. The viral genome is flanked by UTRs and is polycistronic, harboringreplicase ORFs 1a and 1b followed by the genes encoding the envelope proteins, the N protein, and the accessory ORF3 protein. S, spike; E,envelope; M, membrane; N, nucleocapsid. Expression of the ORF1a and 1b yields two known polyproteins (pp1a and pp1ab) by −1 programmedRFS, which are co-translationally or post-translationally processed into at least 16 distinct nsps designated nsp1–16 (bottom). PLpro, papain-likecysteine protease; 3CLpro, the main 3C-like cysteine protease; RdRp; RNA-dependent RNA polymerase; Hel, helicase; ExoN, 3’→ 5’ exonuclease;NendoU, nidovirus uridylate-specific endoribonuclease; 2’OMT, ribose-2’-O-methyltransferase. b Model of PEDV structure. The structure of the PEDVvirion is illustrated on the left. Inside the virion is the RNA genome associated with the N protein to form a long, helical ribonucleoprotein (RNP)complex. The virus core is enclosed by a lipoprotein envelope, which contains S, E, and M proteins. The predicted molecular sizes of each structuralprotein are indicated in parentheses. A set of corresponding sg mRNAs (sg mRNA; 2–6), through which canonical structural proteins or nonstructuralORF3 protein are exclusively expressed via a co-terminal discontinuous transcription strategy, are also depicted on the right

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[54]. PEDV induces apoptotic cell death in vitro andin vivo through the caspase-independent mitochondrialapoptosis-inducing factor (AIF) pathway [55]. PEDV in-fection activates the three major mitogen-activated pro-tein kinase (MAPK) cascades involving extracellularsignaling-regulated kinase (ERK), p38 MAPK, and c-JunN-terminal kinase (JNK) [55, 56] (Kim Y, Lee C, unpub-lished data). In addition, PEDV appears to induce ERstress and activate NF-κB [34, 35]. Therefore, viral repli-cation and subsequent pathological changes rely onPEDV ability to exploit multiple intracellular processes,

such as apoptosis, MAPK signaling, and ER stress, whichemerge in response to various extracellular stimuli.

HeterogeneityCoronaviruses possess the largest known RNA genomes.Nonetheless, they maintain the stability and high fidelityreplication of their large genomes while concomitantlygenerating genetic diversity required for adaptation andemergence. These properties can be ascribed to the 3’-to-5’ proofreading exoribonuclease activity within nsp14[57, 58]. Considering the high fidelity of coronavirus

Fig. 2 Overview of the PEDV replication cycle. PEDV binds pAPN via the spike protein. Penetration and uncoating occur after the S protein-mediatedfusion of the viral envelope with the plasma membrane. Following disassembly, the viral genome is released into the cytoplasm and immediatelytranslated to yield replicases ppla and pp1ab. These polyproteins are proteolytically cleaved into 16 nsps comprising the replication and transcriptioncomplex (RTC) that first engages in the minus-strand RNA synthesis using genomic RNA. Both full- and sg-length minus strands are produced andused to synthesize full-length genomic RNA and sg mRNAs. Each sg mRNA is translated to yield only the protein encoded by the 5’-mostORF of the sg mRNA. The envelope S, E, and M proteins are inserted in the ER and anchored in the Golgi apparatus. The N protein interacts withnewly synthesized genomic RNA to form helical RNP complexes. The progeny virus is assembled by budding of the preformed RNP at the ER-Golgiintermediate compartment (ERGIC) and then released by the exocytosis-like fusion of smooth-walled, virion-containing vesicles with the plasmamembrane [22]

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RNA replication, PEDV is assumed to undergo a slowevolutionary process accumulating mutations or recom-bination events necessary for viral fitness [59]. Geneticand phylogenetic analyses using the whole-genome orsome individual genes have been conducted to deter-mine diversity and relationships of global PEDV isolates.Among these, the full-length S gene and its S1 portion(aa 1–735) have been known to be suitable loci forsequencing to investigate genetic relatedness and mo-lecular epidemiology of PEDV [16, 26, 28, 60, 61].Although only one serotype of PEDV has been reported,phylogenetic studies of the S gene suggested that PEDVcan be genetically separated into 2 groups: genogroup 1(G1; classical) and genogroup 2 (G2; field epidemic orpandemic). Each genogroup can be further divided intosubgroups 1a and 1b, and 2a and 2b, respectively (Fig. 3).G1a includes the prototype PEDV strain CV777, vaccinestrains, and other cell culture-adapted strains, whereasG1b comprises new variants that were first identified inChina [9], later in the United States [62] and SouthKorea [61], and recently in European countries [63–65].G2 contains global field isolates, which are further clus-tered into 2a and 2b subgroups responsible for previouslocal epidemic outbreaks in Asia and recent pandemicoutbreaks in North America and Asia, respectively. Theglobal outbreak of virulent G2b strains appears to haveresulted from point mutations in resident virulent fieldG1a populations.S genes of most PEDV field strains within the G2

group consist of 4161 nucleotides (nt) encoding 1386amino acid (aa) residues. These genes are 9-nt (3-aa)longer than the homologous gene in the prototypeCV777 strain. Compared to the sequences of CV777, G2PEDV strains possess distinct genetic signatures, Sinsertions-deletions (S indels) that involve 2 notable 4-aaand 1-aa insertions at positions 55 and 56 and positions135 and 136, respectively, and a unique 2-aa deletion-located between positions 160 and 161 within the N-terminal hypervariable region of the S protein [26](Fig. 4). In addition, this S indel pattern in G2 strains isidentical to other novel G2 variants, MF3809 [Gen-Bank:KF779469] and FL2013 [GenBank:KP765609],identified in South Korea and China, respectively, whichharbored a large 204-aa S deletion at positions 713–916or a 7-aa S deletion in the C-terminus, respectively(Fig. 4) [66, 67].New variant strains within G1b are genetically diver-

gent from G1a and G2 PEDV strains. Although G1bstrains were isolated from epidemic cases, they do notcontain genetic S signatures typical for G2 field strains.Sequence comparison of the N-terminal one-third of theS gene revealed that G1b strains share more than 95 %of their sequence with G1a classical strains, but theiridentity with G2 epidemic strains is less than 89 %. In

contrast, the analysis of the remaining portion of the Sgene indicated that G1b strains exhibit more than 99 %identity with G2 field strains [61]. Furthermore, the en-tire genome-based phylogenetic analysis showed thatG1b strains are clustered closely together with G2 epi-demic PEDVs (Fig. 3b). Collectively, these data suggestthat novel G1b variants appear to have resulted from arecombination event between classical G1a and epidemicG2 viruses, possibly during viral sg mRNA transcription,which most probably geographically happened in China.The US G1b variants have been named S INDEL strainsbecause of the presence of insertions and a deletion inthe S gene compared to sequences of original US PEDVstrains [15]. This nomenclature might be incorrect sincegenomic sequences of PEDV isolates should be initiallycompared to that of the prototype PEDV strain CV777.Considering this issue, all G2 epidemic isolates includespecific S indels, which make them different fromCV777. It is therefore recommended that those strainsbe termed S INDEL strains.

Molecular epidemiologyEpidemiology of PEDV in EuropeAlthough PEDV first appeared in the United Kingdomand spread to other European countries in the 1970s,the disease impact caused by PEDV in Europe and itseconomic importance were negligible compared to itseffects on the industry in Asian countries and the UnitedStates. Over the last decades, therefore, the presenceof PEDV was not intensely studied. In 1980s and1990s, PEDV outbreaks became infrequent, while thevirus persisted in an endemic form in the pig populationat a low rate. Sporadic outbreaks were reported in someEuropean countries, causing diarrhea in weaner or feederpigs. A number of serological surveys indicated that sero-prevalence of PEDV had become low in European pigs[68–73]. Interestingly, despite low immunity of pigs inEuropean countries, the virus has not been causing severeoutbreaks in these susceptible populations although theexact resistance mechanism has not been elucidated.However, PEDV that affected in pigs of all ages, in-cluding suckling piglets, re-emerged in a typical epi-demic form in Italy in 2006 [74]. In 2014, a case ofPED, which occurred on a fattening farm, was re-ported in Germany [63]. Shortly thereafter, outbreaksof PEDV were identified in a farrow-finish herd inFrance and in fattening pigs in Belgium [64, 65].These German, French, and Belgian PEDV strainswere found to be genetically almost identical to eachother (99.9 % identity) and most closely related toG1b variants identified in China, the United States,and South Korea (Fig. 3). Further surveillance studiesare needed to determine whether the G1b strainshave already been circulating in Europe or were

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recently introduced from the United States or Asia.Since PED outbreaks may occur periodically in thosecountries, the implementation of proper biosecurityprotocols would be necessary in order to prevent

further spread of PEDV domestically or internation-ally in Europe. In addition, it would be important toinvestigate if high virulent G2 PEDV is present incertain areas of Europe.

Fig. 3 Phylogenetic analyses of global PEDV strains based on nucleotide sequences of the spike genes (a) and full-length genomes (b). A putativesimilar region of the spike protein and the complete genome sequence of TGEV was included as an outgroup in each panel. Multiple sequencealignments were performed using ClustalX 2.0 program and the phylogenetic tree was constructed from aligned nucleotide sequences using thedistance-based neighbor-joining method of MEGA5.2 software. Numbers at each branch represent bootstrap values greater than 50 % of 1000replicates. Names of the strains, countries and years of isolation, GenBank accession numbers, genogroups, and subgroups are shown. PEDVisolates identified in different countries are indicated by corresponding symbols: Europe (solid triangles), South Korea (sold circles), Thailand andVietnam, (sold diamonds), and the United States (solid squares). Scale bars indicate nucleotide substitutions per site

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Epidemiology of PEDV in AsiaIn Asia, PED epidemics first occurred in 1982 in Japanand since then, PED caused severe epidemics in adjacentAsian countries, particularly in China and South Korea,resulting in heavy losses of piglets [8, 11, 75]. In the late2000s, PEDV has been reported and become increasinglyproblematic in the Philippines, Thailand, Taiwan, andVietnam [10, 17, 76].In Thailand, several outbreaks of severe PEDV infec-

tion have emerged since late 2007. PEDV isolates re-sponsible for epidemics in Thailand had S geneticsignatures typical for field epidemic G2 strains and wereplaced in the cluster adjoining to South Korean andChinese strains in the G2a or G2b subgroup ([77] seealso Fig. 3a). PED was first observed in southern prov-inces of Vietnam and soon after, the disease spreadthroughout all major swine-producing regions in that

country [76]. Vietnamese strains also had unique S indelcharacteristics and could be classified as the G2b subli-neage, which continues to cause sporadic outbreaks inVietnam [78].PED still remains a devastating enteric disease leading

to serious losses in China since its first identification. Inthe early 1990s, a vaccine containing the inactivatedprototype CV777 strain was developed and has sincebeen widely used throughout the swine industry inChina. Until 2010, outbreaks of PED became infrequentwith only a limited number of incidents. However, aremarkable increase in PED epidemics occurred in pig-producing provinces in late 2010 [9]. During that period,new variants of PEDV belonging to the G1b genogroupwere first reported in China [9]. In addition, PED out-breaks in vaccinated herds questioned the effectivenessof the CV777-based vaccine [9]. Since then, severe

Fig. 4 Amino acid sequence alignment of the N-terminal region of the S protein of global PEDV strains. The top illustration represents the organizationof the PEDV genome. Only the corresponding alignment of amino acid sequences of the N-terminal region containing hypervariable regions [26] isshown. Dashes (−) indicate deleted sequences. Potential N glycosylation sites predicted by GlycoMod Tool (http://www.expasy.ch/tools/glycomod/)are shown in boldface type. Genetic subgroups of PEDV were marked with different colors: G1a (red), G1b (blue), G2a (green), and G2b (black). Insertionsand deletions (indels) within PEDV isolates compared to the prototype CV777 strain are shaded. Amino acids representing potential hypervariabledomains are indicated by solid boxes

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PEDV epidemics have been reported in various regionsin China [79–81]. At present, PED outbreaks in Chinawere caused by both G1b variants and field epidemic G2strains that differed genetically from the prototypeCV777 strain [81]. One of the G2b strains, AH2012, waslater found to be a potential progenitor of US PEDVstrains that emerged subsequently during 2013 [15, 82].Prior to late 2013, the prevalence of PEDV infection

was relatively low with only sporadic outbreaks inTaiwan and Japan. In late 2013, severe large-scale PEDepizootics suddenly re-emerged in these countries,which led to tremendous financial losses in their porkindustry [17, 18]. Taiwan and Japanese isolates during2013 to 2014 were phylogenetically related to the sameclade as global G2b PEDV strains [17, 18].

Epidemiology of PEDV in the United StatesPEDV has been exotic in the United States until its sud-den and explosive emergence in May 2013. Since then,PEDV has spread rapidly in swine farms across theUnited States, causing significant financial losses [14].Genetic and phylogenetic analyses of the emergent USPEDV strains identified during the initial outbreak re-vealed a close relationship with Chinese strains, espe-cially the AH2012 strain isolated in 2012 from AnhuiProvince in China, suggesting their origin [82]. Recently,it was suggested that the emergent PEDV strains in theUnited States potentially descended from 2 Chinesestrains, AH2012 [GenBank:KC210145] and CH/ZMDZY/11 [GenBank:KC196276] in G2b sublineage through re-combination [15, 80]. Furthermore, PEDV strains similarto those found in the United States appear to be respon-sible for subsequent large-scale PED outbreaks in SouthKorea, Taiwan, and Japan in late 2013 [16–18].In January 2014, other novel US PEDV strains, such as

OH851 [GenBank:KJ399978], without typical S proteingenetic signatures of the epidemic G2 virus were re-ported. They phylogenetically clustered closely to novelChinese strains in the G1b subgroup based on the simi-larities of the S gene or with the emergent US PEDVstrains in the G2 group based on the whole genomecharacteristics [62]. Novel variants from the UnitedStates had a low nucleotide identity in their first 1170nucleotides of the S1 region and a high similarity in theremaining S gene, compared to the PEDV strains mainlycirculating in the United States, suggesting a rapid evo-lution of US PEDV variants through possible recombin-ation events [62]. However, a retrospective studydemonstrated that the new US variants were alreadypresent in June 2013, indicating a possibility that mul-tiple parental PEDV strains were introduced into theUnited States at about the same time [15]. Althoughanother PEDV variant TC-PC22A [GenBank:KM392224]with a 197-aa deletion in the N-terminal region of the S

protein was isolated, the large deletion was found tooccur during cell adaptation, suggesting that such vari-ants might not circulate naturally in US swine [50].

Epidemiology of PEDV in South KoreaThe first PED epizootic in South Korea was confirmedin 1992 [8]. However, a retrospective study revealed thatPEDV already existed since as early as 1987 [83]. PEDoutbreaks have since occurred every year and becameendemic, which resulted in high rates of death amongpiglets and substantial economic losses to domesticswine industry until 2010. In a serological survey carriedout in 2007, 91.8 % of 159 tested farms had sero-positivepigs in wean to finish periods (30–150 days of age), indi-cating that the majority of farms were affected with en-demic PEDV infection [84]. Since early 2000s, bothmodified attenuated and inactivated vaccines based ondomestic isolates SM98-1 or DR-13 have been intro-duced nationwide, leading to a decline in the incidenceof PEDV-associated diarrheal disease outbreaks com-pared to the past years. However, continuous PED epi-demics in vaccinated farms have raised problems relatedto the efficacy of Korean commercial vaccines. PED iso-lates, which prevalently circulated in South Korea duringthe same period, were classified as G2a strains that con-tained S indels compared to CV777 and were distantlyrelated to CV777 or Korean vaccine strains belonging tothe G1a subgroup [26].After South Korea experienced severe outbreaks of the

foot-and-mouth disease (FMD) in 2010–2011, there wasa state of lull during PED emergence. The prevalence ofPEDV infections was occasional with only intermittentoutbreaks in South Korea from 2011 to early 2013. Thisepidemic situation likely resulted from the mass cullingof more than 3 million pigs (one-third of the entiredomestic pig population) in South Korea during the2010–2011 FMD outbreaks. However, beginning fromNovember 2013, severe PED epidemics increased re-markably and swept through more than 40 % of pigfarms across mainland South Korea [16]. Four monthslater, PEDV hit Jeju Island, which was PEDV-free since2004 [60]. The re-emergent PEDV isolates responsiblefor massive epidemics in South Korea in 2013–2014were classified into the G2b subgroup, where they clus-tered closely with emergent US PEDV strains [16, 60].The source of PEDV incursion into the South Koreanswine population has not yet been determined. The im-portation of pig breeding stock during or after the sud-den emergence of PEDV in the United States might beone of the possible sources, but it remains unclearwhether G2b PEDVs similar to US strains had pre-existed in South Korea. Indeed, the G2b isolatesKDJN12YG [GenBank:KJ857475] and KNU-1303 [Gen-Bank:KJ451038] have been identified independently in

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November 2012 [59] and May 2013 [16], respectively.The former was similar to Chinese G2b strains, whereasthe latter resembled emergent US G2b strains (Fig. 3a).Given these results, it is also conceivable that the virus,which has evolved independently by recombination orpoint mutations might have already been present inSouth Korea as a minor lineage before the emergence ofoutbreaks in the United States. Alternatively, it mighthave originated directly from China. Under suitable cir-cumstances, G2b strains have subsequently becomedominant, leading to a number of recent acute outbreaksnationwide [16, 59].In March of 2014, novel variant G1b PEDV isolates

have been found in South Korea, which were similar tothe variants reported in China, the United States, andrecently in several European countries [61]. They hadcommon genetic and phylogenetic features of G1bstrains (no S indels compared to CV777, different phylo-genetic subgroup [G1b or G2] depending on the se-quence of the S protein or whole-genome, and evidenceof recombination), and were most closely related to theUS variant strain OH851 among other G1b strains [61].Although a temporal study will be needed to verify thepresence of the G1b virus in earlier periods before itsfirst identification, it is possible that similar to the causesof outbreaks in the United States, 2 G1b and G2b ances-tor strains resembling US strains could have been simul-taneously transmitted into South Korea. Another novelPEDV G2 strain (MF3809) with a large S deletion wasfound in South Korea, however, this isolate was identi-fied from only 3 diarrhea samples out of 2634 on 1 outof 569 farms obtained in 2008 [66]. Thus, probability ofthe existence of this variant in South Korean pigs is verylow at present. Nonetheless, we need to continue sur-veying yet-unidentified PEDV variants that may emergelocally or globally through genetic drift (e.g., after pointmutations) or genetic shift (e.g., recombination events).

TransmissionPEDV infection among pigs occurs principally by a dir-ect or indirect fecal-oral route. Airborne transmissionmay also play a role in PEDV dissemination under cer-tain conditions [85]. PEDV can mainly enter farms bydiarrheal feces or vomitus and contaminated environ-mental sources via clinically or subclinically infectedpigs, trailers (transporting pigs, manures, or food),people (pig owners or visitors, such as swine practi-tioners or trailer drivers in contaminated work clothingand footwear), or wild animals and birds [6, 86]. Othercontaminated fomites, such as sow milk, feed, fooditems, or food additives or ingredients, including spray-dried porcine plasma, could all be potential sources ofthe virus [9, 87–89].

After an acute (epidemic) outbreak, PEDV may dis-appear, remain in the farrowing unit because of inad-equate hygiene management (e.g., improper disinfectionand poor biosecurity), or persist in pigs in weaning orgrowing-finishing units where the virus is circulating,causing mild post-weaning diarrhea with very low mor-tality rates. In this endemic status, if newly born pigs areunable to obtain sufficient levels of maternal immunityfrom their dams due to incomplete sow vaccination ordefective lactation performance owing to mastitis oragalactia, the virus circulating on the farm will infect sus-ceptible piglets, which serve as the source of recurrence ofepidemic outbreaks leading to a high number of pigdeaths [90, 91]. Such endemic PED circumstances are notrestricted to Asia: they may equally happen in NorthAmerica, where sudden PED epidemics recently emerged.

Clinical signs, lesions, and pathogenesisPEDV can infect pigs of all ages, causing watery diarrheaand vomiting accompanied by anorexia and depression.Morbidity approaches 100 % in piglets, but can varyin sows [6]. The incubation period of PEDV is ap-proximately 2 days, ranging from 1 to 8 days depend-ing on field or experimental conditions. The intervalbetween the onset and cessation of clinical signs is3–4 weeks [4, 6, 49, 81, 92, 93]. Fecal shedding ofPEDV can be detected within 48 h and may last forup to 4 weeks. The severity of the disease and mor-tality rates might be inversely associated with the ageof the pigs [6, 94]. PEDV infection in piglets up to1 week of age causes severe watery diarrhea andvomiting for 3–4 days followed by extensive dehydra-tion and electrolyte imbalance leading to death. Mor-tality rate averages 50 %, often approaching 100 % in1- to 3-day-old piglets, and decreases to 10 % there-after. In older animals, including weaner to finisherpigs, clinical signs are self-limiting within 1 weekafter the onset of the disease. However, PED mayaffect growth performance of growing pigs. Sows maynot have diarrhea and often they manifest depressivesymptoms and anorexia. If farrowing sows lose theiroffspring, they may subsequently suffer from repro-ductive disorders including agalactia or delayed estrus,which result from the absence of suckling pigletsduring the lactation period.Gross lesions are confined to the gastrointestinal

tract and characterized by distended stomach filledwith completely undigested milk curd and thin, trans-parent intestine walls with accumulation of yellowishfluids [49, 92, 95]. Histological hallmarks of the PEDVinfection include severe diffuse atrophic enteritis, superfi-cial villous enterocyte swelling with mild cytoplasmicvacuolation, necrosis of scattered enterocytes followed bysloughing, and contraction of the subjacent villous lamina

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propria containing apoptotic cells [49, 92, 93, 95]. Theintestinal villi become reduced to two-thirds or more oftheir original length (villous height to crypt depth ratioschange to less than 3:1 in affected pigs) with the extent ofthe pathology depending on the stage of the infection ordisease process [92, 93, 95].PEDV replicates in the cytoplasm of villous epithelial

cells throughout the small intestine, destroying targetenterocytes as a result of massive necrosis or apoptosis.These processes lead to villous atrophy and vacuolationas well as a marked reduction in the enzymatic activity[6, 55]. This sequence of events interrupts digestion andabsorption of nutrients and electrolytes, thereby causingmalabsorptive watery diarrhea followed by serious andfatal dehydration in piglets [6, 96]. Upon infection withPEDV, the disease outcome and deaths usually occurage-dependently. Although the reasons why PEDVcauses more severe disease in nursing piglets in com-parison to weaned pigs have not been clearly elucidated,slower regeneration of enterocytes in neonatal pigs mayan important factor [97]. PEDV infection increases thenumber of crypt stem cells and proliferation of cryptcells, pointing to the accelerated epithelial cell renewal[98]. Enterocyte turnover rate was slower in normalnursing piglets than in weaned pigs, suggesting that thespeed of crypt stem cell replacement appears to be asso-ciated with the age-dependent resistance to PED [98].

DiagnosisSince signs of the PEDV infection were clinically andpathologically indistinguishable from those caused byTGEV and the recently described porcine deltacorona-virus [96, 99, 100], PED diagnosis cannot be made purelyon the basis of clinical signs and histopathological le-sions. Therefore, differential diagnosis to demonstratethe presence of PEDV and/or its antigens must be con-ducted in the laboratory. A variety of PEDV detectionmethods, which include immunofluorescence (IF) orimmunohistochemistry (IHC) tests, in situ hybridization,electron microscopy, virus isolation, enzyme-linkedimmunosorbent assays (ELISA), and various reverse-transcription polymerase chain reaction (RT-PCR) tech-niques, have been used. Taking into account their fastturnaround times and sensitivity, conventional and real-time RT-PCR systems available as commercial kits aremost widely used for PEDV detection during epidemicor endemic outbreaks, as well as for quarantine orslaughter policies. In addition, nucleotide sequencing ofthe S gene region may be useful in determining thegenotype of PEDV circulating in herds. The combinationof RT-PCR and S gene sequencing could well becomethe optimal tool for monitoring genetic diversity amongPEDV isolates.

A number of serological assays have been used for the de-tection of PEDV antibodies, including indirect fluorescentantibody (IFA) staining, ELISA, and virus neutralization(VN) tests. Due to the special protection strategy (passiveimmunization) for neonatal piglets against PEDV, deter-mining the presence or absence of anti-PEDV antibodiesmay be meaningless in sow herds. Instead, measuring quan-tities (or titers) of neutralizing antibodies against PEDV or,especially, against the S protein in serum and colostrumshould be necessary to monitor the immunity level follow-ing sow immunization. In this regard, VN test could beessential for estimating levels of protective antibodies,which piglets would receive from sows. However, thismethod is time-consuming and cannot selectively detectonly secretory IgA antibodies representing mucosal im-munity. In contrast, IFA and indirect ELISA approaches forantibody detection are equally specific but less time-consuming and easier to perform than VN test. Most assaysthat are currently in use have been developed on the basisof either whole virus [101–103] or viral protein antigens[29, 104]. Whole virus-based IFA and ELISA tests may beinappropriate for detecting protective antibodies regardlessof the antigen (S, M, or N proteins) since they can onlydetect exposure due to natural infection or vaccination.However, these tools may still be useful for monitoringendemic situation with the PEDV infection in affectedfarms by determining infection status in weaner to finisherpigs. On the other hand, the entire S protein or its S1 por-tion could be used as viral antigens for developing ELISAbecause the S1 domain has been reported to contain thereceptor binding region and main neutralizing epi-topes [45, 105]. Recently, a recombinant S1 protein-based indirect ELISA has been developed to detectanti-PEDV antibodies [29]. Although this method is a use-ful, sensitive and specific tool for the detection of anti-PEDV S IgG and IgA antibodies in serum and colostrumsamples, it remains to be determined whether concentra-tions of these antibodies correlate with levels of immuneprotection.

Prevention and control measuresBiosecurityOne of the most important measures for prevention andcontrol of acute PED outbreaks is strict biosecurity thatblocks in principle the entrance of PEDV into pig farms(fattening and farrowing units) by minimizing introduc-tion of any material or any person, which could be incontact with the virus. To accomplish this, disinfectionmust be thoroughly applied to all fomites, personnel,and external visitors that could be contaminated withPEDV. Although PEDV is inactivated by most virucidaldisinfectants [24], PEDV RNA can still be detected byRT-PCR even after disinfection with several commer-cially available disinfectants [106]. Thus, we may need to

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evaluate disinfectants in vivo or under various field con-ditions, especially during the winter season, in order toselect suitable disinfectant compositions and appropriateprocedures. The following order of disinfection steps isrecommended to pork producers attempting to disinfecttransportation equipment or affected farrowing units: (i)proper cleaning by a high pressure washer using warmwater at temperatures over 70 °C; (ii) disinfection by anappropriate disinfectant according to directions on thelabel; and (iii) overnight drying [90, 91]. Other biosecur-ity measures include restricting human traffic betweenfattening and farrowing units and limiting contact be-tween trailers or drivers and the farm interior during theloading process at the pig farm or between drivers andthe slaughter facilities during the unloading process atthe collection point [86, 90, 91]. All newly arriving or re-placement animals including gilts should be isolated fora certain period to monitor their health status [90, 91].PEDV is a transboundary virus that seems to spread

readily to neighboring or distant countries even acrosscontinents. Since PEDV is not a World Organization forAnimal Health reportable disease, quarantine inspectionmight not properly implement potential sources orroutes that mediate virus transmission between coun-tries. During large-scale severe PED epidemics in adja-cent or trading countries, quarantine (or internationalbiosecurity) procedures should be adequately reinforcedwith a particular attention to any risk factors of inter-national disease transmission in order to prevent the

entrance of PEDV as well as other emerging or re-emerging pathogens. On the basis of available geneticand phylogenetic data on global PEDV strains, I proposeseveral prospective paths through which PEDV couldhave spread to Asia and North America (Fig. 5). Theclassical G1a isolates might have emerged in China dueto a careless use of cell-adapted strains as autogenousvaccines or illegal importation of attenuated live vaccinesfrom South Korea. The epidemic G2a South Koreanstrains might have been initially introduced into China.Chinese G2a viruses were later transmitted to SoutheastAsian countries including Thailand and Vietnam. It isalso possible that G2a strains in these countries couldhave been directly transported from South Korea. InChina, novel classical G1b and pandemic G2b virusesappear to have arisen concurrently in late 2010 to early2011 probably via recombination between local G1a andG2a strains or point mutations in resident G2a viruses,respectively. These strains were likely coincidentally in-troduced into the United States. US-like G1b and G2bstrains later landed in South Korea. The genesis of epi-demic G2b strains might be ascribed to the evolutionarydrift in local G2a lineages in South Korea. In addition,US-like G2b viruses spread further to other NorthAmerican countries and also to Taiwan and Japan. Cur-rently, there have been no official reports about theemergence of G1b viruses in these countries. Novel G1band G2b strains may already be present in or they mayyet to be brought to Southeast Asian countries from

Fig. 5 Potential international PEDV transmission routes. Genetic subgroups of PEDV were marked with different colors as described in the legendto Fig. 4. Solid lines indicate PEDV spreads that have already occurred between countries; dotted lines indicate PEDV spreads that are expected tohappen eventually; dashed circular arrows denote genetic mutations or recombination events that lead to the emergence of the novel subtypes

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China or South Korea. Considering this expected inter-national dissemination route, we may recheck the im-portance of quarantine policy against PEDV and otherepizootic agents.

VaccinesVaccination of sows is a fundamental tool in a strategyto control and eradicate PED during epidemic or en-demic outbreaks. Piglets are then protected by a transferof maternal antibodies via colostrum and milk from im-mune dams. Although PED first emerged in Europe, thedisease has not caused sufficient economic losses to jus-tify the vaccine development. In contrast, PED outbreaksin Asian countries have been serious, and therefore sev-eral PEDV vaccines have been developed. In China,CV777-attenuated or -inactivated vaccines have beenroutinely applied against PED. Attenuation of the viru-lence of the Japanese PEDV strain 83P-5 was achievedafter 100 passages in Vero cells [27]. Subsequently, thecell-adapted 83P-5 strain has been employed as an intra-muscular (IM) live virus vaccine (P-5 V) in Japan and itis now also available in South Korea. The cell-cultureadaptation method was also applied to attenuate twoSouth Korean virulent PEDV strains, SM98-1 (93 pas-sages) and DR-13 (100 passages) [107, 108]. The SM98-1strain has been used as an IM live or killed vaccine,whereas DR-13 is available as an oral live vaccine. Al-though these attenuated or inactivated vaccines havebeen demonstrated to provide protection under experi-mental conditions, their effectiveness in the field, as wellas pros and cons of their use, are still being debated. InSouth Korea, the multiple dose vaccination program (3or 4 IM administrations of vaccines in the followingorder: live-killed-killed or live-live-killed-killed, corres-pondingly) at 2- or 3-week intervals starting before far-rowing or mating is commonly recommended inpregnant sows or gilts to maintain high levels of neutral-izing antibodies in serum and colostrum [90, 91].Recently, the Korean Animal and Plant QuarantineAgency evaluated the efficacy of domestic and importedPED vaccines commercially available in South Korea.The administration of each commercial vaccine accord-ing to corresponding manuals (twice at both 3 and5 weeks prior to farrowing) increased the survival rate ofpiglets challenged with a virulent wild-type PEDV from18.2 % to over 80 %. However, all vaccines did not sig-nificantly reduce the morbidity rate of diarrhea includingvirus shedding in feces [109]. Although protectionagainst the enteric disease is primarily dependent on thepresence of secretory IgA antibodies in the intestinalmucosa, the vaccine efficacy might be associated withmaintaining high levels of PEDV-specific neutralizingantibodies in the serum and colostrum of vaccinatedsows [90, 91, 109]. In addition to a direct vaccination,

another crucial aspect is passive colostral and lactogenicimmunity of neonatal piglets by ample quantities of pro-tective antibodies obtained from sow colostrums andmilk. Thus, sanitation and health conditions of lactatingsows have to be monitored to eliminate potential factorsnegatively affecting lactation performance, such as mas-titis or agalactia, so that sows could constantly providehigh-quality colostrum and milk to their litters. Sucklingpiglets lose their source of lactogenic immunity at wean-ing and soon thereafter become vulnerable to PEDV.Following an acute PED epidemic, the virus may persistin susceptible animals or pigs that survived, leading tothe circulation of the virus on the farm (endemic PED).Thus, active immunization of weaner to finisher pigsmay be necessary for the control of endemic PEDVinfections [6].The low to moderate effectiveness of current PEDV

vaccines appears to be due to antigenic, genetic (>10 %amino acid variation between respective S proteins) andphylogenetic (G1 vs. G2) differences between vaccineand field epidemic strains [16, 26, 30, 49, 59]. Therefore,G2b epidemic PEDV or related strains prevalent in thefield should be used for the development of next gener-ation vaccines to control PED. The recombinant S1 pro-tein derived from the field G2 PEDV isolate efficientlyprotected newborn piglets against PEDV, so it could bepotentially used as a subunit vaccine for PED preventionin the future [30]. Isolation of PEDV that is phenotypic-ally and genotypically identical to field strains respon-sible for PED epidemics worldwide is critical fordeveloping effective vaccines. A number of culturablePEDV strains associated with recent outbreaks were ob-tained in the United States [28, 50]. On the basis ofthese isolates, an inactivated PEDV vaccine has beendeveloped, which is currently available on the US mar-ket. It is expected that commercial live attenuated vac-cines will soon be ready for pig producers. In SouthKorea, a field epidemic PEDV strain has been recentlyisolated in my laboratory, and we are now utilizing thisisolate to spur the development of new effective and safevaccines [49]. Interestingly, a recent study indicated thatprevious exposure of sows with “mild” G1b PEDV pro-vides cross-protective lactogenic immunity against pigletchallenge with virulent G2b virus [110]. This findingsuggests that the vaccine or route of administration mayalso affect the efficacy of vaccines. Although it may behard to predict the efficacy of new vaccines in the field,they will be promising practical tools for preventionand/or control of PED if their use is accompanied bytightened biosecurity and optimal farm management.

Alternative immunoprophylactic and therapeutic strategiesIn acute PED outbreaks with rapidly increasing mortalityrates, we may consider intentional exposure (feedback)

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of pregnant sows to the autogenous virus using wateryfeces or minced intestines from infected neonatal piglets,which will artificially stimulate rapid lactogenic immun-ity and, hopefully, shorten the outbreak on the farm [6].However, there are several complications that need to beconsidered before the application of this approach.Wide-spread circulation of other viral pathogens, such asPRRSV or PCV2, contained in the intestinal or fecal con-tents may occur among sows or piglets [111, 112]. Sinceautogenous viral materials do not have homogenous infec-tious titers of PEDV, sow immunity may not be induced toa level sufficient for offspring protection. Following artifi-cial exposure of sows, infectious viruses will be shed infeces, which, in turn, could be a potential source for PEDVtransmission within the contaminated establishment andbetween different farms.Artificial passive immunization by oral administration of

specific antibodies represents an attractive approachagainst gastrointestinal pathogens such as PEDV. Chickenegg yolk immunoglobulin against PEDV or the S1 domainhas been found to protect neonatal piglets following chal-lenge exposure [113, 114]. The immunoprophylactic effectof colostrum from cows immunized with PEDV has alsoled to a reduced mortality in newborn piglets [115]. Singlechain variable fragments (scFvs) of the mouse monoclonalantibody or E. coli expressing scFvs were verified toneutralize PEDV in vitro [116]. This suggests that recom-binant E. coli harboring scFvs might be an alternativeprophylactic measure against PEDV infection. Pharmaco-logical, biological, or natural agents that shorten epithelialcell renewal by stimulating proliferation or reorganizationof crypt stem cells could be potential therapeutic targets toreduce PEDV-associated mortality from dehydration fol-lowing severe villous atrophy [98]. For instance, the epider-mal growth factor (EGF) has been shown to stimulateproliferation of intestinal crypt epithelial cells and to miti-gate atrophic enteritis induced in piglets by PEDV infec-tion. This finding suggested that treatment with EGF couldbe another therapeutic option [117]. Broad-spectrum anti-viral drugs, such as ribavirin, which suppress PEDV infec-tion in vitro, are of interest for their potential to treat PED[53]. Chemical inhibitors as well as compounds from medi-cinal plants or natural sources, which block the activationof mitochondrial AIF or MAPK signaling pathways re-quired for PEDV replication, could be new therapeuticcandidates to reduce PEDV-associated symptoms and mor-tality [55, 56]. In addition, nutritional supplements, whichreduce stress and enhance resistance to the disease, may beuseful for PED control in neonatal piglets.

ConclusionsFor the last two or three decades, PED has continued toplague the pork industry in Europe and Asia. In early2013, the disease struck North America resulting in

great economic losses, especially in the United States.Shortly thereafter, massive nationwide PED outbreaksreoccurred in South Korea, Japan, and Taiwan. PED isnow globally recognized as an emerging and re-emergingdisease and it has become a major financial issue for theswine industry worldwide. Despite geographically limitedPED studies in Europe and Asia, a better knowledge ofthe virology, pathogenesis, immunology, epidemiology,and vaccinology has been gained. Since the emergence ofPED in North America, much has been learned fromresearch in the United States. Nevertheless, further studiesare warranted to decipher the virus and the associated dis-ease, and more extensive academic and practical studiesare needed for a comprehensive understanding of themolecular and pathogenic biology of PEDV in order todevelop effective vaccines and establish control measuresincluding biosecurity in affected areas. Lastly, we shouldbear in mind that a combined application of vaccines, bio-security protocols, and husbandry management must bethe key step to prevent and control PED. Integrated andcoordinated efforts in various disciplines among re-searchers, swine veterinarians, producers, swine industryspecialists, producer associations, and authorities arerequired to achieve effective implementation of necessarymeasures.

Competing interestsThe authors declare that they have no competing interests.

Authors’ contributionsCL drafted and wrote the manuscript, and designed the artwork. All authorsread and approved the finalmanuscript.

AcknowledgmentsI thank Ms. Sunhee Lee for her assistance in the preparation of references andfigures. This paper was supported by Bio-industry Technology DevelopmentProgram through the Korea Institute of Planning and Evaluation for Technologyin Food, Agriculture, Forestry and Fisheries (iPET) funded by the Ministry ofAgriculture, Food and Rural Affairs (315021–04).

Received: 6 August 2015 Accepted: 10 November 2015

References1. Oldham J. Letter to the editor. Pig Farming. 1972;10:72–3.2. Chasey D, Cartwright SF. Virus-like particles associated with porcine

epidemic diarrhea. Res Vet Sci. 1978;25:255–6.3. Wood EN. An apparently new syndrome of porcine epidemic diarrhoea. Vet

Rec. 1977;100:243–4.4. Pensaert MB, de Bouck P. A new coronavirus-like particle associated with

diarrhea in swine. Arch Virol. 1978;58:243–7.5. Debouck P, Pensaert M. Experimental infection of pigs with a new porcine

enteric coronavirus, CV777. Am J Vet Res. 1980;41:219–23.6. Saif LJ, Pensaert MB, Sestack K, Yeo SG, Jung K. Coronaviruses. In: Straw BE,

Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, editors.Diseases of Swine. Ames: Wiley-Blackwell; 2012. p. 501–24.

7. Chen JF, Sun DB, Wang CB, Shi HY, Cui XC, Liu SW, et al. Molecularcharacterization and phylogenetic analysis of membrane protein genesof porcine epidemic diarrhea virus isolates in China. Virus Genes. 2008;36:355–64.

8. Kweon CH, Kwon BJ, Jung TS, Kee YJ, Hur DH, Hwang EK, et al. Isolation ofporcine epidemic diarrhea virus (PEDV) in Korea. Korean J Vet Res. 1993;33:249–54 (in Korean).

Lee Virology Journal (2015) 12:193 Page 13 of 16

9. Li W, Li H, Liu Y, Pan Y, Deng F, Song Y, et al. New variants of porcineepidemic diarrhea virus, China, 2011. Emerg Infect Dis. 2012;8:1350–3.

10. Puranaveja S, Poolperm P, Lertwatcharasarakul P, Kesdaengsakonwut S,Boonsoongnern A, Urairong K, et al. Chinese-like strain of porcine epidemicdiarrhea virus. Thailand Emerg Infect Dis. 2009;15:1112–5.

11. Takahashi K, Okada K, Ohshima K. An outbreak of swine diarrhea of a new-type associated with coronavirus-like particles in Japan. Jpn J Vet Sci. 1983;45:829–32.

12. Mole B. Deadly pig virus slips through US borders. Nature. 2013;499:388.13. Ojkic D, Hazlett M, Fairles J, Marom A, Slavic D, Maxie G, et al. The

first case of porcine epidemic diarrhea in Canada. Can Vet J. 2015;56:149–52.

14. Stevenson GW, Hoang H, Schwartz KJ, Burrough ER, Sun D, Madson D,et al. Emergence of porcine epidemic diarrhea virus in the UnitedStates: Clinical signs, lesions, and viral genomic sequences. J Vet DiagnInvest. 2013;25:649–54.

15. Vlasova AN, Marthaler D, Wang Q, Culhane MR, Rossow KD, Rovira A, etal. Distinct characteristics and complex evolution of PEDV strains, NorthAmerica, May 2013–February 2014. Emerg Infect Dis. 2014;20:1620–8.

16. Lee S, Lee C. Outbreak-related porcine epidemic diarrhea virus strainssimilar to US strains, South Korea, 2013. Emerg Infect Dis. 2014;20:1223–6.

17. Lin CN, Chung WB, Chang SW, Wen CC, Liu H, Chien CH, et al. US-like strainof porcine epidemic diarrhea virus outbreaks in Taiwan, 2013–2014. J VetMed Sci. 2014;76:1297–9.

18. MAFF. Ministry of agriculture, Forestry, and Fisheries, Japan. www.maff.go.jp/j/syouan/douei/ped/ped.html. 2013. Accessed 20 Jul 2015 (in Japanese).

19. Cavanagh D. Nidovirales: A new order comprising Coronaviridae andArteriviridae. Arch Virol. 1997;142:629–33.

20. Kocherhans R, Bridgen A, Ackermann M, Tobler K. Completion of theporcine epidemic diarrhoea coronavirus (PEDV) genome sequence. VirusGenes. 2001;23:137–44.

21. Duarte M, Tobler K, Bridgen A, Rasschaert D, Ackermann M, Laude H.Sequence analysis of the porcine epidemic diarrhea virus genome betweenthe nucleocapsid and spike protein genes reveals a polymorphic ORF.Virology. 1994;198:466–76.

22. Lai MC, Perlman S, Anderson LJ. Coronaviridae. In: Knipe DM, Howley PM,Griffin DE, Martin MA, Lamb RA, Roizman B, Straus SE, editors. Fields Virology.5th ed. Philadelphia: Lippincott Williams & Wilkins; 2007. p. 1306–36.

23. Hofmann M, Wyler R. Quantitation, biological and physicochemicalproperties of cell culture-adapted porcine epidemic diarrhea coronavirus(PEDV). Vet Microbiol. 1989;20:131–42.

24. Pospischil A, Stuedli A, Kiupel M. Diagnostic notes update on porcineepidemic diarrhea. J Swine Health Prod. 2002;10:81–5.

25. Jackwood MW, Hilt DA, Callison SA, Lee CW, Plaza H, Wade E. Spikeglycoprotein cleavage recognition site analysis of infectious bronchitis virus.Avian Dis. 2001;45:366–72.

26. Lee DK, Park CK, Kim SH, Lee C. Heterogeneity in spike protein genesof porcine epidemic diarrhea viruses isolated in Korea. Virus Res. 2010;149:175–82.

27. Sato T, Takeyama N, Katsumata A, Tuchiya K, Kodama T, Kusanagi K.Mutations in the spike gene of porcine epidemic diarrhea virus associatedwith growth adaptation in vitro and attenuation of virulence in vivo. VirusGenes. 2011;43:72–8.

28. Chen Q, Li G, Stasko J, Thomas JT, Stensland WR, Pillatzki AE, et al. Isolationand characterization of porcine epidemic diarrhea viruses associated withthe 2013 disease outbreak among swine in the United States. J ClinMicrobiol. 2014;52:234–43.

29. Gerber PF, Gong Q, Huang YW, Wang C, Holtkamp D, Opriessnig T. Detectionof antibodies against porcine epidemic diarrhea virus in serum and colostrumby indirect ELISA. Vet J. 2014;202:33–6.

30. Oh J, Lee KW, Choi HW, Lee C. Immunogenicity and protective efficacy ofrecombinant S1 domain of the porcine epidemic diarrhea virus spikeprotein. Arch Virol. 2014;159:2977–87.

31. de Haan CA, Vennema H, Rottier PJ. Assembly of the coronavirus envelope:Homotypic interactions between the M proteins. J Virol. 2000;74:4967–78.

32. Zhang Z, Chen J, Shi H, Chen X, Shi D, Feng L, et al. Identification of aconserved linear B-cell epitope in the M protein of porcine epidemicdiarrhea virus. Virol J. 2012;9:225.

33. Baudoux P, Carrat C, Besnardeau L, Charley B, Laude H. Coronaviruspseudoparticles formed with recombinant M and E proteins induce alphainterferon synthesis by leukocytes. J Virol. 1998;72:8636–43.

34. Xu X, Zhang H, Zhang Q, Dong J, Liang Y, Huang Y, et al. Porcineepidemic diarrhea virus E protein causes endoplasmic reticulum stressand up-regulates interleukin-8 expression. Virol J. 2013;10:26.

35. Xu X, Zhang H, Zhang Q, Huang Y, Dong J, Liang Y, et al. Porcine epidemicdiarrhea virus N protein prolongs S-phase cell cycle, induces endoplasmicreticulum stress, and up-regulates interleukin-8 expression. Vet Microbiol.2013;164:212–21.

36. McBride R, van Zyl M, Fielding BC. The coronavirus nucleocapsid is amultifunctional protein. Viruses. 2014;6:2991–3018.

37. Ding Z, Fang L, Jing H, Zeng S, Wang D, Liu L, et al. Porcine epidemicdiarrhea virus nucleocapsid protein antagonizes beta interferon productionby sequestering the interaction between IRF3 and TBK1. J Virol. 2014;88:8936–45.

38. Song DS, Yang JS, Oh JS, Han JH, Park BK. Differentiation of a Vero celladapted porcine epidemic diarrhea virus from Korean field strains byrestriction fragment length polymorphism analysis of ORF 3. Vaccine. 2003;21:1833–42.

39. Wang K, Lu W, Chen J, Xie S, Shi H, Hsu H, et al. PEDV ORF3 encodes an ionchannel protein and regulates virus production. FEBS Lett. 2012;586:384–91.

40. Woo PC, Lau SK, Lam CS, Lau CC, Tsang AK, Lau JH, et al. Discovery of sevennovel Mammalian and avian coronaviruses in the genus deltacoronavirussupports bat coronaviruses as the gene source of alphacoronavirus andbetacoronavirus and avian coronaviruses as the gene source ofgammacoronavirus and deltacoronavirus. J Virol. 2012;86:3995–4008.

41. McVey DS, Kennedy M, Chengappa MM. Veterinary Microbiology. 3rd ed.Ames: Wiley-Blackwell; 2013.

42. Reguera J, Mudgal G, Santiago C, Casasnovas JM. A structural view ofcoronavirus-receptor interactions. Virus Res. 2014;194:3–15.

43. Li BX, Ge JW, Li YJ. Porcine aminopeptidase N is a functional receptor forthe PEDV coronavirus. Virology. 2007;365:166–72.

44. Nam E, Lee C. Contribution of the porcine aminopeptidase N (CD13)receptor density to porcine epidemic diarrhea virus infection. Vet Microbiol.2010;144:41–50.

45. Lee DK, Cha SY, Lee C. The N-terminal region of the porcine epidemicdiarrhea virus spike protein is important for the receptor binding. KoreanJ Microbiol Biotechnol. 2011;39:140–5.

46. Hofmann M, Wyler R. Propagation of the virus of porcine epidemic diarrheain cell culture. J Clin Microbiol. 1988;26:2235–9.

47. Lawrence PK, Bumgardner E, Bey RF, Stine D, Bumgarner RE. Genomesequences of porcine epidemic diarrhea virus: In vivo and in vitrophenotypes. Genome Announc. 2014;2:e00503.

48. Huan CC, Wang Y, Ni B, Wang R, Huang L, Ren XF, et al. Porcine epidemicdiarrhea virus uses cell-surface heparan sulfate as an attachment factor.Arch Virol. 2015;160:1621–8.

49. Lee S, Kim Y, Lee C. Isolation and characterization of a Korean porcineepidemic diarrhea virus strain KNU-141112. Virus Res. 2015;208:215–24.

50. Oka T, Saif LJ, Marthaler D, Esseili MA, Meulia T, Lin CM, et al. Cell cultureisolation and sequence analysis of genetically diverse US porcine epidemicdiarrhea virus strains including a novel strain with a large deletion in thespike gene. Vet Microbiol. 2014;173:258–69.

51. Shirato K, Matsuyama S, Ujike M, Taguchi F. Role of proteases in therelease of porcine epidemic diarrhea virus from infected cells. J Virol.2011;85:7872–80.

52. Wicht O, Li W, Willems L, Meuleman TJ, Wubbolts RW, van Kuppeveld FJ, etal. Proteolytic activation of the porcine epidemic diarrhea coronavirus spikefusion protein by trypsin in cell culture. J Virol. 2014;88:7952–61.

53. Kim Y, Lee C. Ribavirin efficiently suppresses porcine nidovirus replication.Virus Res. 2013;171:44–53.

54. Zeng S, Zhang H, Ding Z, Luo R, An K, Liu L, et al. Proteome analysis ofporcine epidemic diarrhea virus (PEDV)-infected Vero cells. Proteomics.2015;15:1819–28.

55. Kim Y, Lee C. Porcine epidemic diarrhea virus induces caspase-independentapoptosis through activation of mitochondrial apoptosis-inducing factor.Virology. 2014;460–461:180–93.

56. Kim Y, Lee C. Extracellular signal-regulated kinase (ERK) activation is requiredfor porcine epidemic diarrhea virus replication. Virology. 2015;484:181–93.

57. Smith EC, Denison MR. Implications of altered replication fidelity on theevolution and pathogenesis of coronaviruses. Curr Opin Virol. 2012;2:519–24.

58. Smith EC, Denison MR. Coronaviruses as DNA wannabes: A new model forthe regulation of RNA virus replication fidelity. PLoS Pathog. 2013;9:e1003760.

Lee Virology Journal (2015) 12:193 Page 14 of 16

59. Kim SH, Lee JM, Jung J, Kim IJ, Hyun BH, Kim HI, et al. Genetic characterizationof porcine epidemic diarrhea virus in Korea from 1998 to 2013. Arch Virol.2015;160:1055–64.

60. Lee S, Ko DH, Kwak SK, Lim CH, Moon SU, Lee DS, et al. Reemergence ofporcine epidemic diarrhea virus on Jeju Island. Korean J Vet Res. 2014;54:185–8.

61. Lee S, Park GS, Shin JH, Lee C. Full-genome sequence analysis of a variantstrain of porcine epidemic diarrhea virus in South Korea. Genome Announc.2014;2:e01116.

62. Wang L, Byrum B, Zhang Y. New variant of porcine epidemic diarrhea virus,United States, 2014. Emerg Infect Dis. 2014;20:917–9.

63. Hanke D, Jenckel M, Petrov A, Ritzmann M, Stadler J, Akimkin V, et al.Comparison of porcine epidemic diarrhea viruses from Germany and theUnited States, 2014. Emerg Infect Dis. 2015;21:493–6.

64. Grasland B, Bigault L, Bernard C, Quenault H, Toulouse O, Fablet C, et al.Complete genome sequence of a porcine epidemic diarrhea S gene indelstrain isolated in France in December 2014. Genome Announc. 2015;3:e00535.

65. Theuns S, Conceição-Neto N, Christiaens I, Zeller M, Desmarets LM,Roukaerts ID, et al. Complete genome sequence of a porcine epidemicdiarrhea virus from a novel outbreak in Belgium, january 2015. GenomeAnnounc. 2015;3:e00506.

66. Park S, Kim S, Song D, Park B. Novel porcine epidemic diarrhea virus variantwith large genomic deletion. South Korea Emerg Infect Dis. 2014;20:2089–92.

67. Zhang X, Pan Y, Wang D, Tian X, Song Y, Cao Y. Identification andpathogenicity of a variant porcine epidemic diarrhea virus field strain withreduced virulence. Virol J. 2015;12:88.

68. Carvajal A, Lanza I, Diego R, Rubio P, Cármenes P. Seroprevalence of porcineepidemic diarrhea virus infection among different types of breeding swinefarms in Spain. Prev Vet Med. 1995;1–2:33–40.

69. Pijpers A, van Nieuwstadt AP, Terpstra C, Verheijden JH. Porcine epidemicdiarrhoea virus as a cause of persistent diarrhoea in a herd of breeding andfinishing pigs. Vet Rec. 1993;132:129–31.

70. Nagy B, Nagy G, Meder M, Mocsári E. Enterotoxigenic Escherichia coli,rotavirus, porcine epidemic diarrhoea virus, adenovirus and calici-like virusin porcine postweaning diarrhoea in Hungary. Acta Vet Hung. 1996;44:9–19.

71. Pensaert MB, Van Reeth K. Porcine epidemic diarrhea and porcinerespiratory coronavirus. Proc Am Assoc Swine Practitioners. 1998; 433–6.

72. Pritchard GC, Paton DJ, Wibberley G, Ibata G. Transmissible gastroenteritisand porcine epidemic diarrhoea in Britain. Vet Rec. 1999;144:616–8.

73. Van Reeth K, Pensaert M. Prevalence of infections with enzootic respiratoryand enteric viruses in feeder pigs entering fattening herds. Vet Rec. 1994;135:594–7.

74. Martelli P, Lavazza A, Nigrelli AD, Merialdi G, Alborali LG, Pensaert MB.Epidemic of diarrhoea caused by porcine epidemic diarrhoea virus in Italy.Vet Rec. 2008;162:307–10.

75. Jinghui F, Yijing L. Cloning and sequence analysis of the M gene of porcineepidemic diarrhea virus LJB/03. Virus Genes. 2005;30:69–73.

76. Duy DT, Toan NT, Puranaveja S, Thanawongnuwech R. Geneticcharacterization of porcine epidemic diarrhea virus (PEDV) isolates fromsouthern Vietnam during 2009–2010 outbreaks. Thai J Vet Med. 2011;41:55–64.

77. Temeeyasen G, Srijangwad A, Tripipat T, Tipsombatboon P, Piriyapongsa J,Phoolcharoen W, et al. Genetic diversity of ORF3 and spike genes of porcineepidemic diarrhea virus in Thailand. Infect Genet Evol. 2014;21:205–13.

78. Vui DT, Tung N, Inui K, Slater S, Nilubol D. Complete genome sequence ofporcine epidemic diarrhea virus in Vietnam. Genome Announc. 2014;2:e00753.

79. Sun RQ, Cai RJ, Chen YQ, Liang PS, Chen DK, Song CX. Outbreak of porcineepidemic diarrhea in suckling piglets. China Emerg Infect Dis. 2012;18:161–3.

80. Tian PF, Jin YL, Xing G, Qv LL, Huang YW, Zhou JY. Evidence of recombinantstrains of porcine epidemic diarrhea virus, United States, 2013. Emerg InfectDis. 2014;20:1735–8.

81. Wang XM, Niu BB, Yan H, Gao DS, Yang X, Chen L, et al. Genetic propertiesof endemic Chinese porcine epidemic diarrhea virus strains isolated since2010. Arch Virol. 2013;158:2487–94.

82. Huang YW, Dickerman AW, Piñeyro P, Li L, Fang L, Kiehne R, et al. Origin,evolution, and genotyping of emergent porcine epidemic diarrhea virusstrains in the United States. MBio. 2013;4:e00737.

83. Park NY, Lee SY. Retrospective study of porcine epidemic diarrhea virus(PEDV) in Korea by in situ hybridization. Korean J Vet Res. 1997;37:809–16(in Korean).

84. Park CK, Pak SI. Infection patterns of porcine epidemic diarrhea virus (PEDV)by sera-epidemiological analysis in Korean pig farms. J Life Sci. 2009;19:1304–8 (in Korean).

85. Alonso C, Goede DP, Morrison RB, Davies PR, Rovira A, Marthaler DG, et al.Evidence of infectivity of airborne porcine epidemic diarrhea virus anddetection of airborne viral RNA at long distances from infected herds. VetRes. 2014;45:73.

86. Lowe J, Gauger P, Harmon K, Zhang J, Connor J, Yeske P, et al. Role oftransportation in spread of porcine epidemic diarrhea virus infection. UnitedStates Emerg Infect Dis. 2014;20:872–4.

87. Dee S, Clement T, Schelkopf A, Nerem J, Knudsen D, Christopher-Hennings J,et al. An evaluation of contaminated complete feed as a vehicle for porcineepidemic diarrhea virus infection of naïve pigs following consumption vianatural feeding behavior: Proof of concept. BMC Vet Res. 2014;10:176.

88. Opriessnig T, Xiao CT, Gerber PF, Zhang J, Halbur PG. Porcine epidemicdiarrhea virus RNA present in commercial spray-dried porcine plasma is notinfectious to naïve pigs. PLoS One. 2014;9:e104766.

89. Pasick J, Berhane Y, Ojkic D, Maxie G, Embury-Hyatt C, Swekla K, et al.Investigation into the role of potentially contaminated feed as a sourceof the first-detected outbreaks of porcine epidemic diarrhea in Canada.Transbound Emerg Dis. 2014;61:397–410.

90. Park CK, Lee C. Clinical examination and control measures in a commercialpig farm persistently infected with porcine epidemic diarrhea virus. J VetClin. 2009;26:463–6 (in Korean).

91. Park CK, Lee KK, Lee C. PED past, present, and future. Proc Asian Pig Vet SocCongr. 2011; S19–20.

92. Jung K, Wang Q, Scheuer KA, Lu Z, Zhang Y, Saif LJ. Pathology of USporcine epidemic diarrhea virus strain PC21A in gnotobiotic pigs. EmergInfect Dis. 2014;20:662–5.

93. Madson DM, Magstadt DR, Arruda PH, Hoang H, Sun D, Bower LP, et al.Pathogenesis of porcine epidemic diarrhea virus isolate (US/Iowa/18984/2013) in 3-week-old weaned pigs. Vet Microbiol. 2014;174:60–8.

94. Shibata I, Tsuda T, Mori M, Ono M, Sueyoshi M, Uruno K. Isolation of porcineepidemic diarrhea virus in porcine cell cultures and experimental infectionof pigs of different ages. Vet Microbiol. 2000;72:173–82.

95. Debouck P, Pensaert M, Coussement W. The pathogenesis of an entericinfection in pigs, experimentally induced by the coronavirus-like agent,CV777. Vet Microbiol. 1981;6:157–65.

96. Ducatelle R, Coussement W, Debouck P, Hoorens J. Pathology ofexperimental CV777 coronavirus enteritis in piglets II Electron microscopicstudy. Vet Pathol. 1982;19:57–66.

97. Moon HW, Norman JO, Lambert G. Age dependent resistance totransmissible gastroenteritis of swine (TGE). I. Clinical signs and somemucosal dimensions in small intestine. Can J Comp Med. 1973;37:157–66.

98. Jung K, Saif LJ. Porcine epidemic diarrhea virus infection: Etiology,epidemiology, pathogenesis and immunoprophylaxis. Vet J. 2015;204:134–43.

99. Haelterman EO. On the pathogenesis of transmissible gastroenteritis ofswine. J Am Vet Med Assoc. 1972;160:534–40.

100. Ma Y, Zhang Y, Liang X, Lou F, Oglesbee M, Krakowka S, et al. Origin,evolution, and virulence of porcine deltacoronaviruses in the United States.MBio. 2015;6:e00064.

101. Carvajal A, Lanza I, Diego R, Rubio P, Cármenes PJ. Evaluation of a blockingELISA using monoclonal antibodies for the detection of porcine epidemicdiarrhea virus and its antibodies. J Vet Diagn Invest. 1995;7:60–4.

102. Hofmann M, Wyler R. Enzyme-linked immunosorbent assay for thedetection of porcine epidemic diarrhea coronavirus antibodies in swinesera. Vet Microbiol. 1990;21:263–73.

103. Oh JS, Song DS, Yang JS, Song JY, Moon HJ, Kim TY, et al. Comparison of anenzyme-linked immunosorbent assay with serum neutralization test forserodiagnosis of porcine epidemic diarrhea virus infection. J Vet Sci. 2005;6:349–52.

104. Knuchel M, Ackermann M, Müller HK, Kihm U. An ELISA for detection ofantibodies against porcine epidemic diarrhoea virus (PEDV) based on thespecific solubility of the viral surface glycoprotein. Vet Microbiol. 1992;32:117–34.

105. Sun DB, Feng L, Shi HY, Chen JF, Liu SW, Chen HY, et al. Spike proteinregion (aa 636–789) of porcine epidemic diarrhea virus is essential forinduction of neutralizing antibodies. Acta Virol. 2007;51:149–56.

106. Bowman AS, Nolting JM, Nelson SW, Bliss N, Stull JW, Wang Q, et al. Effectsof disinfection on the molecular detection of porcine epidemic diarrheavirus. Vet Microbiol. 2015;179:213–8.

Lee Virology Journal (2015) 12:193 Page 15 of 16

107. Kweon CH, Kwon BJ, Lee JG, Kwon GO, Kang YB. Derivation of attenuatedporcine epidemic diarrhea virus (PEDV) as vaccine candidate. Vaccine. 1999;17:2546–53.

108. Song DS, Oh JS, Kang BK, Yang JS, Moon HJ, Yoo HS, et al. Oral efficacy ofVero cell attenuated porcine epidemic diarrhea virus DR13 strain. Res VetSci. 2007;82:134–40.

109. QIA. Animal and Plant Quarantine Agency, Republic of Korea. 2014.http://www.qia.go.kr/viewwebQiaCom.do?id=36111&type=6_18_1bdsm.Accessed 11 July 2014 (in Korean).

110. Goede D, Murtaugh MP, Nerem J, Yeske P, Rossow K, Morrison R. Previousinfection of sows with a “mild” strain of porcine epidemic diarrhea virusconfers protection against infection with a “severe” strain. Vet Microbiol.2015;176:161–4.

111. Jung K, Ha Y, Ha SK, Kim J, Choi C, Park HK, et al. Identification of porcinecircovirus type 2 in retrospective cases of pigs naturally infected withporcine epidemic diarrhoea virus. Vet J. 2006;171:166–8.

112. Park JS, Ha Y, Kwon B, Cho KD, Lee BH, Chae C. Detection of porcinecircovirus 2 in mammary and other tissues from experimentally infectedsows. J Comp Pathol. 2009;140:208–11.

113. Kweon CH, Kwon BJ, Woo SR, Kim JM, Woo GH, Son DH, et al.Immunoprophylactic effect of chicken egg yolk immunoglobulin (Ig Y)against porcine epidemic diarrhea virus (PEDV) in piglets. J Vet Med Sci.2000;62:961–4.

114. Lee DH, Jeon YS, Park CK, Kim SJ, Lee DS, Lee C. Immunoprophylactic effectof chicken egg yolk antibody (IgY) against a recombinant S1 domain of theporcine epidemic diarrhea virus spike protein in piglets. Arch Virol. 2015;160:2197–207.

115. Shibata I, Ono M, Mori M. Passive protection against porcine epidemicdiarrhea (PED) virus in piglets by colostrum from immunized cows. J VetMed Sci. 2001;63:655–8.

116. Pyo HM, Kim IJ, Kim SH, Kim HS, Cho SD, Cho IS, et al. Escherichia coliexpressing single-chain Fv on the cell surface as a potential prophylacticof porcine epidemic diarrhea virus. Vaccine. 2009;27:2030–6.

117. Jung K, Kang BK, Kim JY, Shin KS, Lee CS, Song DS. Effects of epidermalgrowth factor on atrophic enteritis in piglets induced by experimentalporcine epidemic diarrhoea virus. Vet J. 2008;177:231–5.

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